Shaft assemblies in reciprocating internal combustion engines are typically comprised of shafts with meshing gears that are supported by bearings placed in the engine oil base and engine cylinder block. Unfortunately, the accumulation of tolerances in the base, the gasket between the block and base, the shafts and the gears can result in a gap between the shaft and the bearings. This gap allows the shaft to move axially during engine operation, causing increased engine wear, engine noise and the possible chucking of the gears.
In addition to the initial gap which may be present, gaps between the shafts and bearings can change during engine operation. Because different materials are used for different components of the assembly, the gaps will change as the temperature in the engine changes because of the different thermal expansion rates of the components. External forces that are exerted on the shaft, for example by the gears, will also affect the size of the gap and these forces can vary with engine speed.
One method that is currently used to eliminate this gap is to place shims between the shaft and bearings with thicknesses equal to the gap. Unfortunately, the use of shims does not eliminate the entire gap, but only reduces the gap. The insertion of shims during assembly is also very time consuming, requiring the assembler to use a special measuring device to measure the exact gap that will result in each shaft/bearing assembly for each engine. The problems with using shims is magnified for field service personnel who do not have the same measuring devices but must select new shims whenever a component is changed. Moreover, the use of shims does not address the movement of the shaft caused by thermal expansion and external forces on the shafts.
A second method that could be used to eliminate the gap would be to use compressible spacers similar to those described in U.S. Pat. Nos. 4,492,018 and 4,611,935. A compressible spacer with a thickness that is greater than the maximum gap that could arise from the accumulated design tolerances would be placed on the shaft. When the engine is assembled, the spacer would be compressed to the proper thickness. Unfortunately, this method does not address the movement of the shaft due to thermal expansion and external forces. Therefore, the shaft could move during engine operation to create a gap or the shaft could move to further compress the spacer which would result in a gap when the shaft moved back during other operating conditions. Moreover, this method can produce undesirable high inward loads on the shaft.
A third method that could be used to eliminate the gaps would be to size each shaft for a specific engine block, engine base and bearing arrangement. Unfortunately, this method does not address the movement of the shaft due to thermal expansion and external forces. Moreover, a new shaft would be needed each time a block, oil base or bearing was changed and a new block or oil base may be needed if a shaft were changed. Therefore, the problems of field service personnel and the cost of repairs would be increased.
Therefore, there arises a need for a method of assembling a shaft assembly in a reciprocating internal combustion engine that eliminates any gaps created due to the accumulation of design tolerances and that reduces the movement of the shaft caused by thermal expansion or external forces.